Androgen receptor assays have been performed on 1371 specimens of histologically confirmed primary and recurrent breast cancer. Forty-two patients who had received tamoxifen as treatment for advanced disease were assessed for objective response. Another 42 patients who had received chemotherapy were similarly studied. Patients with androgen receptor-negative tumors had a significantly poorer response rate to hormone therapy than those with receptor-positive tumors (P less than 0.05). This clinical correlation is supported by survival data of 1181 patients with primary breast cancer which showed that patients with androgen receptor-negative tumors had a highly significant trend toward shorter overall survival than those with receptor-positive tumors (P less than 0.001). Androgen receptor data added significantly to the information provided by estrogen receptor data both in terms of response to hormone treatment and survival.